The present invention generally relates to a solid-state imaging device, and a method for driving the solid-state imaging device and also to a solid-state imaging camera. More specifically, the present invention is directed to a solid-state imaging device suitably employed as an imaging device in a picture (imaging) appliance such as a video camera and an electronic still camera, and to a method for driving such a solid-state imaging device, and also to a camera equipped with such a solid-state imaging device.
A conventional solid-state imaging apparatus used in a video camera and the like, for example, a CCD (charge-coupled device) solid-state imaging device, may realize the interlaced scanning operation by a so-called xe2x80x9cfield reading out methodxe2x80x9d since the interlace-mode output signal is produced. As indicated in FIG. 1, signal charges which are stored in a sensor unit 101 only during {fraction (1/60)} seconds (equivalent to 1 field period) and are read out from the respective sensor units 101 are mixed with each other between two pixels positioned adjacent to each other along the vertical direction in a vertical CCD 102, and then the mixed signal charges are outputted. Also, the mixing combination of the two pixels positioned adjacent to each other along the vertical direction is varied every field.
In this field reading out method, the storage time of the signal charge in each of the pixels is equal to {fraction (1/60)} seconds. This storage time becomes a half, as shown in FIG. 2, as compared with that of a so-called xe2x80x9cframe reading out methodxe2x80x9d. In this frame reading out method, the signal charge in the odd line and the signal charge in the even line are alternately read out within storage time of {fraction (1/30)} seconds every field. Therefore, this field reading out method owns an advantage that moving pictures can be imaged under better condition. To the contrary, since the signal charges of the two pixels are mixed with each other along the vertical direction, this field reading out method owns such a drawback that the vertical resolution is lowered. As a consequence, this field reading out method is not suitable as in imaging method for an electronic still camera requiring high vertical resolution.
Under such a circumstance, very recently, electronic still cameras employ a so-called xe2x80x9call-pixel reading out type CCD solid-state imaging devicexe2x80x9d. In this all-pixel reading out type CCD solid-state imaging device, as represented in FIG. 3, the signal charges of the respective pixels are not mixed with each other in the vertical CCD, but are independently read out at the same time instant. In accordance with this all-pixel reading out type CCD imaging device, it is possible to realize the vertical resolution two times higher than that of the above-explained field reading out type solid-state imaging device, assuming now that the total pixel quantity of the all-pixel reading out type CCD imaging device is equal to that of the field reading out type CCD imaging device. To the contrary, this all-pixel reading out type CCD solid-state imaging device would require the output time of the imaging signal two times longer than that of the field reading out type CCD imaging device.
On the other hand, monitors for displaying imaged pictures thereon are normally provided with electronic still cameras in order to perform focusing controls and/or camera angle controls during imaging operations. In an electronic still camera equipped with a so-called xe2x80x9call-pixel reading out type CCD solid-state imaging devicexe2x80x9d as an imaging device, since an output operation of an imaging signal requires twice longer time than that of another reading out type CCD solid-state imaging device in order to display an image on a monitor, the imaging signal must be outputted at high speed.
To this purpose, a so-called xe2x80x9cthinning read out drive operationxe2x80x9d has been proposed by the Applicant in Japanese Laid-open Patent Application No. Hei-8-78315 opened in 1996 as the method capable of outputting the imaging signals at high speed in the all-pixel reading out type CCD solid-state imaging device. In this CCD solid-state imaging device, the signal charges are read out only from a portion of the pixel columns along the vertical direction. In this thinning read out drive operation, the charges are left in the thinned pixel columns. As a consequence, considering now such a case that the reading out operation is transferred from the thinning read out mode to the all-pixel read out mode, there are some possibilities that these left signal charges are mixed with the signal charges read out during the all-pixel read out drive operation.
The present invention has been made to solve the above-described problems, and therefore, has an object to provide a solid-state imaging device and a drive method thereof, and also a solid-state imaging device camera, capable of acquiring signal charges of the respective pixels read out in the all-pixel read out mode when signal reading out operation is transferred from the thinning read out mode to the all-pixel read out mode, while avoiding such a problem that the signal charges left during the thinning read out drive operation are mixed with the signal charges read out during the all-pixel read out drive operation.
A solid-state imaging device, according to an aspect of the present invention, is arranged by comprising: a solid-state imaging element capable of being selectively operable in an all-pixel read out mode where signal charges of all pixels are independently read out at the same time instant, and in a thinning read out mode where signal charges are read out only from a portion of pixel columns along the vertical direction; and a timing generating circuit for generating at least one piece of a signal charge sweeping-out pulse used to discharge the signal charges of the respective pixels just after the signal charges are read out during an exposing time period immediately before a read out operation is transferred from the thinning read out mode to the all-pixel read out mode.
Also, according to another aspect of the present invention, a method for driving a solid-state imaging device equipped with a solid-state imaging element capable of being selectively operable in an all-pixel read out mode where signal charges of all pixels are independently read out at the same time instant, and in a thinning read out mode where signal charges are read out only from a portion of pixel columns along the vertical direction, is featured by that in an exposing time period immediately before a read out operation is transferred from the thinning read out mode to the all-pixel read out mode, the signal charges of the respective pixels are discharged at least one time immediately after the signal charges are read out.
A further aspect of the present invention, a camera is featured by comprising: a solid-state imaging device including a solid-state imaging element capable of being selectively operable in an all-pixel read out mode where signal charges of all pixels are independently read out at the same time instant, and in a thinning read out mode where signal charges are read out only from a portion of pixel columns along the vertical direction; and a timing generating circuit for generating at least one piece of a signal charge sweeping-out pulse used to discharge the signal charges of W the respective pixels just after the signal charges are read out during an exposing time period immediately before a read out operation is transferred from the thinning read out mode to the all-pixel read out mode; and an optical system for conducting incident light to an imaging area of the solid-state imaging device.
In the solid-state imaging device, the driving method thereof, and the camera with employment of the above-described featured arrangement, since at least one piece of the charge sweeping-out pulse is produced just after the signal charges are read out during the exposing time period immediately before the read out mode is transferred from the thinning read out mode to the all-pixel read out mode, such signal charges can be discharged. That is, these signal charges have not been read out from the thinned pixel columns during the thinning read out drive operation, and thus are left therein. As a consequence, when the read out operation is transferred to the all-pixel read out drive operation, it is possible to avoid such an adverse influence caused by that the left signal charges during the thinning read out drive operation are mixed with the signal charges read out during this all-pixel read out drive operation.